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Many shark species have been overexploited for international markets, including fins for shark fin soup in Southeast Asia. Previous studies highlighted the value of large, threatened shark species, regulated under CITES Appendix II. However, sampling biases may have overlooked small shark species. Here, we address this by identifying species from ~4000 small shark fins in Hong Kong. These fins included species not recorded in previous surveys, raising the market's species diversity to 106. Nearly 75% of the small fins came from small shark species and 58.1% of small species were threatened with extinction. We identified an important CITES listing gap: Trade in 19 small, threatened species, especially from the family Triakidae, is unregulated. In addition, a quarter of small fins come from large sharks, indicating that substantial exploitation of juveniles is occurring and may be affecting fisheries sustainability. Enhanced surveillance of small shark fin trade is essential to ensure effective conservation under emerging trade regulations. [ABSTRACT FROM AUTHOR]

Objective: The Gulf of Mexico (GOM) reef bottom longline fishery typically not only targets groupers and snappers but also interacts with 27 species of sharks, which are primarily discarded as bycatch. Slow growth, late maturity, and low fecundity in a landscape of increasing fishing pressure make sharks comparatively more susceptible to overfishing and endangered status than other fishes. The purpose of this study was to determine which gear and/or environmental variables best predict the shark catch per set for commonly caught shark species in the GOM reef bottom longline fishery. Methods: We considered 12 commonly caught shark species that vary from the abundant Atlantic Sharpnose Shark Rhizoprionodon terraenovae to the critically endangered Scalloped Hammerhead Sphyrna lewini. Catch per set, effort, gear, and environmental data were taken from the National Oceanic and Atmospheric Administration National Marine Fisheries Service observer dataset for the GOM reef bottom longline fishery (2009–2017) and were used to fit generalized additive models. The Bayesian information criterion and 10‐fold cross‐validation were used to select the best set of variables that predicted catch per set to determine gear configurations, fisher activities, and environmental conditions contributing to higher shark catch per unit effort. We modeled each species individually, all species combined, and species grouped by similar ecology. Result: Gear and fishing method variables were consistently included in the best predictive models across species and were the only potential basis for a single strategy that could decrease bycatch across all 12 species. Patterns of environmental variables were only consistent across species with similar ecology and habitat. Conclusion: Sharks as a group should not be lumped together, as the effects of mitigation measures become confounded and directly managing trade‐offs between species when minimizing bycatch becomes impossible. Focusing on gear rather than environmental variables is the best apparent option to potentially reduce shark catch per set across commonly caught species while minimizing trade‐offs. Impact statementSharks are slow‐growing species that give birth to very few offspring late in life, making them highly susceptible to overfishing. We used catch data from the Gulf of Mexico to determine gear and environmental conditions that contribute to high shark catch in an attempt to minimize incidental shark catch and prevent overfishing. Focusing on gear configurations is the best apparent option to potentially reduce shark incidental catch across commonly caught species. [ABSTRACT FROM AUTHOR]

Sexual dimorphisms are generated by divergent processes, such as natural or sexual selection and niche convergence. Males and females of the lesser guitarfish, Zapteryx brevirostris, present morphological differences in their discs, and the relationships with the species biology and ecology were unrecognized. Analysing the morphometry of 201 specimens and the influence of bottom features on the frequencies of 188 specimens among life stages and sexes, we found strong evidence that gonadal maturation leads to dimorphisms on discs, validating a concavity on male pectoral fins as a secondary sexual dimorphism and rejecting the hypothesis that such dimorphisms were related to ecological pressures. The principal component analysis (PCA) and permutational MANOVA (PERMANOVA) analyses revealed that males and females shared similar body aspects until they reached maturity, mainly due to lower variations in WD, WR, LD, DPRO, and LSC at younger life stages. The relationships of these variables with LT corroborate the former results, showing a changing point around LT > 30 cm where females started to attain larger measurements than males. Moreover, we revealed ontogenetic shifts, with adults from both sexes exploring different habitats than juveniles and subadults. Differences in frequencies of each life stage were best explained by organic matter (OM) with the adults exploring bottom habitats of higher concentrations of OM than juveniles and subadults, strengthening the assumption that body differences between sexes are not related to ecological pressures. These results bring not only new insights about the possible advantages that those morphometric differences provide to males while mating but also information about the abiotic influences on species distribution, which, along with knowledge of local oceanographic dynamics and benthic community patterns, would inform actions for species conservation. [ABSTRACT FROM AUTHOR]

Bulk stable isotope analysis was used to assess the trophic level and foraging habitats of Caribbean reef sharks (Carcharhinus perezi) compared to three large sympatric predatory teleosts (the Nassau grouper Epinephelus striatus, black grouper Mycteroperca bonaci, and great barracuda Sphyraena barracuda) in an isolated Caribbean coral reef ecosystem. Models and empirical studies have suggested that the depletion of large-bodied sharks in coral reef ecosystems triggers a trophic cascade that could affect the benthic community, favoring algae over coral. The hypothesized cascade is based on the premise that sharks prey on large piscivorous teleost fish that in turn prey on key herbivorous fish. Analysis of nitrogen-stable isotopes ([delta][sup.15]N) from white muscle tissue revealed neither adult or juvenile Caribbean reef sharks were significantly enriched in [sup.15]N compared with sympatric predatory teleost species. Linear regression found no evidence of an ontogenetic increase in nitrogen with increasing body size for Caribbean reef sharks; however, there was a significant positive relationship between body size and carbon isotope ([delta][sup.13]C) values. These results suggest that Caribbean reef sharks in isolated systems do not act as the apex predator in coral reef ecosystems primarily feeding on large-bodied sympatric teleosts. Instead, Caribbean reef sharks form part of an upper trophic-level predator guild alongside large-bodied teleosts, which makes the predicted trophic cascade as a result of the removal of reef sharks unlikely. Moreover, the body size-[delta][sup.13]C relationship suggests Caribbean reef sharks exhibit ontogenetic and individual variation in where they feed. The ecological role of this species is, therefore, complex and contextual, similar to carcharhinid species in the Indo-Pacific, emphasizing the need to further elucidate the interactions between reef sharks and the overall coral reef ecosystem so as to best inform effective conservation and management of the species., Introduction Pristine coral reef ecosystems contain a rich diversity of large predators, including barracuda (F. Sphyraenidae), grouper (F. Serranidae), and sharks (primarily from F. Carcharhinidae). By virtue of their relatively [...]

A management strategy evaluation (based on five species in the California, USA, nearshore fishery) of control rules that reduce relative fishing effort as a function of the ratio of fish density outside versus inside no-take marine reserves (as a measure of depletion) showed that although the control rules allowed effort to increase at first, in the long term, they were effective at maintaining spawning stock biomass and yield for all simulated species, including depleted ones. Scenarios with fish movement, illegal fishing in the reserve, or post-dispersal density dependence in recruitment required higher density ratio targets, such as 60% of mature fish or 80% of all fish, to avoid stock depletion. The effort allowed by multispecies density-ratio control rules depended on the relative weight given to more or less depleted species. High variability in recruitment or in monitoring data caused the allowable effort to fluctuate. Density-ratio control rules have the advantages that they require no historical data, they can be used at local spatial scales, and they adjust to changing environmental conditions. Nous avons evalue la strategie de gestion applique a cinq especes dans la peche commerciale pres de la cote de la Californie, E.-U., concernant les regles de controle qui reduisent l'effort relatif de peche en fonction du rapport entre la densite des poissons a l'exterieur et a l'interieur de reserves marines a peche interdite (comme mesure d'epuisement); il apparait que, bien que les regles de controle permettent un accroissement de l'effort de peche au debut, elles sont efficaces a long terme pour maintenir la biomasse du stock reproducteur et le rendement chez toutes les especes qui ont ete l'objet d'une simulation, meme celles qui souffrent d'epuisement. Les scenarios qui comprennent des deplacements des poissons, de la peche illegale dans la reserve ou une densite-dependance apres la dispersion necessitent des cibles avec des rapports de densite plus eleves, par exemple, 60 % pour les poissons matures ou 80 % pour l'ensemble des poissons, afin d'eviter l'epuisement des stocks. L'effort permis d'apres les regles de controle des rapports de densites appliquees a plusieurs especes depend du poids relatif donnee aux especes plus ou moins epuisees. Une forte variabilite dans le recrutement ou dans les donnees de surveillance entraine une fluctuation dans l'effort permis. Les regles de controle basees sur les rapports de densites ont l'avantage de ne necessiter aucune donneee historique, de pouvoir s'appliquer aux eechelles spatiales locales et de s'ajuster aux conditions environnementales changeantes. [Traduit par la Redaction], Introduction Fishery management attempts to achieve a relatively large sustainable yield while limiting the risk of severe population declines due to inadvertent overfishing. This is often accomplished through the use [...]